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Related Concept Videos

Staphylococcal Skin Infections01:29

Staphylococcal Skin Infections

Staphylococcus aureus is a Gram-positive coccus that resides harmlessly on the skin and mucous membranes of healthy individuals. When the skin barrier is breached, it can shift from a commensal to an opportunistic pathogen. This transition is facilitated by surface adhesins, such as clumping factor B and S. aureus surface protein G (SasG), which bind to structural proteins, including loricrin and cytokeratin, in the damaged epidermis. Protein A, another key factor, binds the Fc region of...
Clinical Significance of Antibiotic Resistance01:25

Clinical Significance of Antibiotic Resistance

Methicillin-resistant Staphylococcus aureus (MRSA) presents a critical public health threat, arising from its capacity to resist β-lactam antibiotics due to acquisition of the mecA gene within the staphylococcal cassette chromosome mec (SCCmec). This gene encodes penicillin-binding protein 2a (PBP2a), which impairs binding efficacy of methicillin and other β-lactams. MRSA has evolved into distinct clonal lineages impacting humans and animals alike, reinforcing its significance within the One...
Mechanism of Antibiotic Resistance in MRSA01:25

Mechanism of Antibiotic Resistance in MRSA

Antibiotic resistance in bacteria arises when microorganisms evolve the ability to withstand drugs designed to kill them or inhibit their growth, rendering once-effective treatments useless. This phenomenon, driven by genetic change and selection under antibiotic exposure, poses a profound threat to modern medicine. Mechanisms include drug-inactivating enzymes (e.g., β-lactamases), efflux pumps that eject antibiotics, mutations altering antibiotic targets, decreased drug uptake, and acquisition...
Determinants of Bacterial Pathogenicity and Virulence01:20

Determinants of Bacterial Pathogenicity and Virulence

Pathogenic bacteria employ a variety of strategies to establish infections, including the secretion of extracellular enzymes that act as potent virulence factors. These enzymes facilitate bacterial colonization of host tissues and help evade immune surveillance. By targeting structural components of host tissues and interfering with immune mechanisms, these enzymes play a pivotal role in disease progression.Extracellular Enzymes Facilitating Tissue Invasion: Several bacterial pathogens secrete...
Gene Regulation in Microbial Communities: Quorum Sensing01:28

Gene Regulation in Microbial Communities: Quorum Sensing

Quorum sensing is a mechanism of bacterial communication that enables coordinated gene expression in response to changes in population density. This facilitates collective behaviors that enhance survival, resource acquisition, and ecological adaptation. This process relies on small signaling molecules called autoinducers that accumulate as bacterial populations grow. When a critical threshold concentration of autoinducers is reached, bacterial cells collectively modify gene expression,...

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Related Experiment Video

Updated: Jul 3, 2026

A Fluorescence-based Method to Study Bacterial Gene Regulation in Infected Tissues
07:10

A Fluorescence-based Method to Study Bacterial Gene Regulation in Infected Tissues

Published on: February 19, 2019

agr function in clinical Staphylococcus aureus isolates.

Katrina E Traber1, Elsie Lee1, Sarah Benson2

  • 1Molecular Pathogenesis Program and Department of Microbiology and Medicine, Helen L. and Martin S. Kimmel Center for Biology and Medicine at the Skirball Institute for Biomolecular Medicine, New York University School of Medicine, 540 First Avenue, NY 10016, USA.

Microbiology (Reading, England)
|August 1, 2008
PubMed
Summary
This summary is machine-generated.

The accessory gene regulator (agr) in Staphylococcus aureus can mutate during infection, leading to agr-defective strains. These agr(-) variants may cooperate with agr(+) strains in infections.

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Development and Assessment of Intracellular Infection Models for Staphylococcus aureus
08:32

Development and Assessment of Intracellular Infection Models for Staphylococcus aureus

Published on: January 17, 2025

Related Experiment Videos

Last Updated: Jul 3, 2026

A Fluorescence-based Method to Study Bacterial Gene Regulation in Infected Tissues
07:10

A Fluorescence-based Method to Study Bacterial Gene Regulation in Infected Tissues

Published on: February 19, 2019

Development and Assessment of Intracellular Infection Models for Staphylococcus aureus
08:32

Development and Assessment of Intracellular Infection Models for Staphylococcus aureus

Published on: January 17, 2025

Area of Science:

  • Microbiology
  • Bacterial genetics
  • Infectious diseases

Background:

  • The accessory gene regulator (agr) controls virulence factors in Staphylococcus aureus.
  • agr is crucial for virulence in animal models and presumed important in human infections.
  • Most clinical S. aureus isolates are agr(+), but agr-defective mutants have been reported.

Purpose of the Study:

  • To investigate if agr-defective mutants isolated from patients arise during infection or post-isolation.
  • To determine the prevalence and origin of agr mutations in clinical S. aureus isolates.

Main Methods:

  • Isolated new staphylococcal strains from clinical infections.
  • Handled isolates carefully to prevent post-isolation mutations.
  • Phenotypic analysis (e.g., haemolysis) and genotypic analysis of agr locus functionality.

Main Results:

  • Identified non-haemolytic strains with agr locus mutations and others with mutations elsewhere.
  • Observed heterogeneous populations with both agr(+) and agr(-) variants in isolates.
  • Found evidence suggesting agr(-) variants arise during the infection process.

Conclusions:

  • Non-haemolytic, agr-defective S. aureus strains are present in human infections.
  • agr(-) variants can emerge during infection, not solely due to lab artifacts.
  • agr(+) and agr(-) variants might interact cooperatively during infections.